Bug 1081322: add string for new contacts phone number editing. r=mattn

browser/locales/en-US/chrome/browser/loop/loop.properties

@@ -97,6 +97,7 @@ new_contact_button=New Contact
 ## and click the 'New Contact' button to see the fields.
 new_contact_name_placeholder=Name
 new_contact_email_placeholder=Email
+new_contact_phone_placeholder=Firefox OS Phone
 
 contacts_blocked_contacts=Blocked Contacts